The growth factor granulin interacts with cyclin T1 and modulates P-TEFb-dependent transcription.
Cyclin T1, together with the kinase CDK9, is a component of the transcription elongation factor P-TEFb which binds the human immunodeficiency virus type 1 (HIV-1) transactivator Tat. P-TEFb facilitates transcription by phosphorylating the carboxy-terminal domain (CTD) of RNA polymerase II. Cyclin T1 is an exceptionally large cyclin and is therefore ... a candidate for interactions with regulatory proteins. We identified granulin as a cyclin T1-interacting protein that represses expression from the HIV-1 promoter in transfected cells. The granulins, mitogenic growth factors containing repeats of a cysteine-rich motif, were reported previously to interact with Tat. We show that granulin formed stable complexes in vivo and in vitro with cyclin T1 and Tat. Granulin bound to the histidine-rich domain of cyclin T1, which was recently found to bind to the CTD, but not to cyclin T2. Binding of granulin to P-TEFb inhibited the phosphorylation of a CTD peptide. Granulin expression inhibited Tat transactivation, and tethering experiments showed that this effect was due, at least in part, to a direct action on cyclin T1 in the absence of Tat. In addition, granulin was a substrate for CDK9 but not for the other transcription-related kinases CDK7 and CDK8. Thus, granulin is a cellular protein that interacts with cyclin T1 to inhibit transcription.
Mesh Terms:
3T3 Cells, Amino Acid Sequence, Animals, Blotting, Western, COS Cells, Cell Line, Cyclin T, Cyclin-Dependent Kinase 8, Cyclin-Dependent Kinase 9, Cyclin-Dependent Kinases, Cyclins, Dose-Response Relationship, Drug, Gene Products, tat, Glutathione Transferase, Humans, Immunoblotting, Intercellular Signaling Peptides and Proteins, Mice, Microscopy, Fluorescence, Models, Genetic, Molecular Sequence Data, Peptides, Phosphorylation, Plasmids, Positive Transcriptional Elongation Factor B, Precipitin Tests, Protein Binding, Protein Structure, Tertiary, Protein-Serine-Threonine Kinases, Recombinant Fusion Proteins, Sequence Homology, Amino Acid, Transcription, Genetic, Transfection, Tumor Cells, Cultured, Two-Hybrid System Techniques, U937 Cells, Viral Proteins
3T3 Cells, Amino Acid Sequence, Animals, Blotting, Western, COS Cells, Cell Line, Cyclin T, Cyclin-Dependent Kinase 8, Cyclin-Dependent Kinase 9, Cyclin-Dependent Kinases, Cyclins, Dose-Response Relationship, Drug, Gene Products, tat, Glutathione Transferase, Humans, Immunoblotting, Intercellular Signaling Peptides and Proteins, Mice, Microscopy, Fluorescence, Models, Genetic, Molecular Sequence Data, Peptides, Phosphorylation, Plasmids, Positive Transcriptional Elongation Factor B, Precipitin Tests, Protein Binding, Protein Structure, Tertiary, Protein-Serine-Threonine Kinases, Recombinant Fusion Proteins, Sequence Homology, Amino Acid, Transcription, Genetic, Transfection, Tumor Cells, Cultured, Two-Hybrid System Techniques, U937 Cells, Viral Proteins
Mol. Cell. Biol.
Date: Mar. 01, 2003
PubMed ID: 12588988
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